1. Field of the Invention
This invention relates to semiconductor fabrication and, in particular, to an improved method for creating a mask pattern of an integrated circuit (IC) for use in lithographic processing.
2. Description of Related Art
Integrated circuits are fabricated by lithographic techniques, where energy beams transmit integrated circuit images or patterns on photomasks to photosensitive resists on semiconductor wafer substrates. The circuit image on the photomask may not be reproduced precisely on the substrate, in part because of optical effects among transmitted and blocked energy passing through the photomask. Optical proximity correction (OPC) has been employed as a key enabling resolution enhancement technique required to meet image size control requirements imposed by state-of-the-art integrated circuit product programs. OPC is essentially the deliberate and proactive distortion of photomask patterns to compensate for systematic and stable errors.
The mask patterns for the elements corresponding to the desired integrated circuit design may be made by a mask writer. A mask writer is typically a variable shaped electron beam tool, such as that available from JEOL Ltd. of Tokyo, Japan. Integrated circuit shapes can be patterned on a semiconductor wafer by the photomask made with an electron beam tool. The mask elements corresponding to portions of a design of an integrated circuit layout are generally made of opaque materials deposited on a quartz substrate.
Typically, designs for the mask elements are made by the following procedure: 1) create the design based on design manual rules; 2) run design rule checks (DRC) on the design data; 3) update the design if any problems are found; 4) run the DRC-clean data through OPC; 5) run the post-OPC data through OPC verification (sometimes referred to as ORC); 6) update the design and/or OPC process if any problems are found; 7) run the final post-OPC data through mask rule checks (MRC); 8) update the design and/or OPC process if any problems are found; and 9) run the DRC/ORC/MRC-clean data through fracturing for the mask writer. These steps are, more or less, run sequentially with potential re-running of various steps as noted above.
The designs for the mask elements are generally made using polygonal shapes. OPC deals with edges of the polygons. Mask fracturing techniques convert those polygons into primitive shapes, generally simple rectangles that can be written by the mask writer. Often the mask writer will be able to resolve larger shapes better than smaller shapes. Long, thin shapes, referred to herein as “slivers,” that are generated by the fracturing software may resolve poorly when the mask writer attempts to create the sliver shape for the photomask. If the sliver is small enough, e.g., in the thickness dimension, it may essentially not resolve at all.